Whitson thundered away from remote Kazakhstan aboard a Russian Soyuz rocket Wednesday with cosmonaut Yuri Malenchenko and Malaysian space tourist Sheikh Muszaphar Shukor. Their spacecraft was on course for a linkup with the space station Friday.

Meanwhile, mission commander Pam Melroy climbed aboard the shuttle Discovery with six colleagues at the Kennedy Space Center in Florida early Wednesday.

Melroy's crew rehearsed the countdown for their October launch on a crucial 14-day assembly mission to the orbital base.

Whitson, who'll be the first woman to command the space station, and Melroy, the second to command a shuttle flight, will meet in orbit if Discovery's missions remain on schedule.

Five years ago this month, the two women met aboard the space station while earning their professional stripes. Whitson was serving a 185-day tour as the station's flight engineer and science officer. Melroy was the shuttle pilot on her second space station assembly flight.

"I look forward to their arrival," Whitson said of Melroy's crew on the eve of her own launch from the Baikonur Cosmodrome. "She thinks it will be a special moment."

Melroy was just as eager about the meeting.

"We are like a family. This is fun for us," Melroy said this week. "The most important thing to me is the picture we take when our hands first meet across the hatches (separating the shuttle and station)."

Whitson, a 47-year-old biochemist who earned her doctorate from Rice University, was selected for astronaut training in 1996. The 2002 mission was her first.

Melroy, 46, recently retired from the U.S. Air Force as a test pilot and was chosen for the astronaut corps in 1994. She first flew as the shuttle's pilot in 2000, a year after Eileen Collins became the first woman to command a space shuttle mission.

The orbital meeting between Whitson and Melroy is largely a coincidence, according to NASA. This year, Melroy's 14-day shuttle mission was originally scheduled for an August liftoff. However, hail storm damage to a shuttle fuel tank in February forced the space agency to push its missions back three months.

During their six months aboard the space station, Whitson and Malenchenko will supervise a critical transformation. Additions of European Space Agency and Japanese science modules late this year and in early 2008 will convert an outpost largely made up of American, Russian and Canadian hardware into a compound representing the efforts of 15 nations.

Discovery's mission will add a gateway module to which the new labs can be attached.

"Their mission is very complex, very challenging," said NASA deputy administrator Shana Dale, who led the U.S. delegation to Whitson's liftoff in Russia. "Under Peggy's leadership, I know they will be able to accomplish all the hard tasks out in front of them."